NASA Logo

NTRS

NTRS - NASA Technical Reports Server

Back to Results
Preliminary Parallaxes of 40 L and T Dwarfs from the US Naval Observatory Infrared Astronometry ProgramWe present preliminary trigonometric parallaxes and proper motions for 22 L dwarfs and 18 T dwarfs measured using the ASTROCAM infrared imager on the US naval Observatory (USNO) 1.55 m Strand Astrometric Reflector. The results presented here are based on observations obtained between 2000 September and 2002 November; about half of the objects have an observational time baseline of t 1:3 yr and half t 2:0 yr. Despite these short time baselines, the astrometric quality is sufficient to produce significant new results, especially for the nearer T dwarfs. Seven objects are in common with the USNO optical CCD parallax program for quality control and seven in common with the European Southern Observatory 3.5 m New Technology Telescope parallax program. We compare astrometric quality with both of these programs. Relative to absolute parallax corrections are made by employing Two Micron All Sky Survey and/or Sloan Digital Sky Survey photometry for reference-frame stars. We combine USNO infrared and optical parallaxes with the best available California Institute of Technology (CIT) system photometry to determine MJ , MH, and MK values for 37 L dwarfs between spectral types L0 and L8 and 19 T dwarfs between spectral types T0.5 and T8 and present selected absolute magnitude versus spectral type and color diagrams, based on these results. Luminosities and temperatures are estimated for these objects. Of special interest are the distances of several objects that are at or near the L-T dwarf boundary so that this important transition can be better understood. The previously reported early to mid T dwarf luminosity excess is clearly confirmed and found to be present at J, H, and K. The large number of objects that populate this luminosity-excess region indicate that it cannot be due entirely to selection effects. The T dwarf sequence is extended to MJ 16:9 by 2MASS J041519 0935, which, at d 5:74 pc, is found to be the lluminous LOG (L=L )pa
Document ID
20040084515
Document Type
Reprint (Version printed in journal)
Authors
Vrba, F. J.
Henden, A. A.
Liginbuhl, C. B.
Guetter, H. H.
Munn, J. A.
Date Acquired
August 21, 2013
Publication Date
May 1, 2004
Subject Category
Astronomy
Report/Patent Number
AD-A424036
Funding Number(s)
CONTRACT_GRANT: HST-HF-01137.01
CONTRACT_GRANT: NAS5-26555
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
Keywords
L DWARFS
STELLAR MOTION
STELLAR PARALLAXES
T DWARFS
INFRARED ASTROMETRY
Document Inquiry

Available Downloads

There are no available downloads for this record.
No Preview Available